Many light-emitting sources have light intensity distribution characteristics which are more conveniently depicted by a graph showing a variation of light intensity with reference to radial angles in lateral directions, as described for example in US 2006-0034097A1.
Semiconductor light-emitting devices are finding increasingly more applications in modern day electronic devices. Typical semi-conductor light-emitting sources, for example, packaged light-emitting diodes (LED), are directional and have a characteristic optical axis along which light is propagated. Typically, the light intensity of an LED follows a Lambert distribution as depicted in FIG. 27 of US 2006-0034097A1. More particularly, a substantial portion of the entire light energy emitted by an LED is contained within an angular range centered about the optical axis and the angular range is commonly referred to as the “viewing angle” of an LED. The viewing angle ranges of an LED are typically between +/−15° to +/−60° about the optical axis.
In many applications involving the use of semiconductor light-emitting devices, it is desirable to condition the optical output of a light-emitting source to suit various objectives. For example, a typical liquid crystal (LCD) display is equipped with a backlight apparatus which comprises an array of LEDs for illuminating an LCD panel from behind since the LCD display panel is not self-illuminating. An example of such a backlight apparatus is described in US 2005-0243576A1. In general, a display panel comprises a plurality of parallel light guides onto which optical output from an array of light-emitting sources are coupled. An illustrative diagram of a display comprising a light guide assembly (10) and an array of edge-lighting LEDs (20) with a typical LED-to-LED pitch of 2-10 mm are depicted in FIGS. 1 and 1A. The entirety of the illuminated light guide assembly defines a useful display area (14).
In such or other similar applications, it is desirable to mix optical outputs from a plurality of light-emitting sources, for example, LEDs (20) of the three primary colours, red (R), green (G) and blue (B), to prepare for forward transmission to light guide (12). The mixing of light from a plurality of LEDs, for example, LEDs emitting the three primary colours is advantageous, since by separating the LEDs into a plurality of distributed locations and then by mixing light from the plurality of distributed sources, problems associated with the high power dissipation and the consequential thermal loading of a high power discrete white LED can be alleviated. However, typical distribution characteristics of a typical LED means that a relatively large distance, compared to the length of a display panel, will be required for light mixing. Therefore, it will be highly desirable if there can be provided optical arrangements for reducing the light mixing distance between a plurality of LED.
Furthermore, with the ever increasing LED power efficiency (lumen/watt), the number of LEDs required for each display will decrease significantly therefore the LED-to-LED pitch is substantially increased. However, an increase in the LED-to-LED pitch will also require an increase of the light mixing area, as depicted schematically in FIGS. 2, 2A and 2B with an exemplary LED-LED pitch (d) of more than 10 mm.
An exemplary optical arrangement for conditioning outputs of an LED for forward transmission is described in U.S. Pat. No. 6,598,998. However, such an arrangement requires a double molding process and still requires has relatively long light mixing distance. Another example of such an optical arrangement is described in US 2006-0034097A1 in which the lens has a relatively complicated structure and the light mixing distance is still relatively long.
Therefore, it will be desirable if there can be provided lens and light-emitting assemblies which would mitigate shortcomings of the known art.